Photo-alignment material and liquid crystal display device and its manufacturing method using the same

ABSTRACT

A photo-alignment material, a liquid crystal display device using the photo-alignment material, and a manufacturing method. The photo-alignment material is a polymer having a photo-reactive ethenyl group on a main chain. When used as a photo-alignment layer, the photo-alignment material enables improved alignment stability against external shocks, light, and heat. The liquid crystal display device includes a first substrate, a second substrate, a liquid crystal layer formed between the first and second substrates, and a photo-alignment layer formed at least on the first substrate, with the photo-alignment layer formed from a photo-alignment material having an ethenyl group at a main chain.

This application is a divisional of U.S. patent application Ser. No.09/893,977 filed Jun. 29, 2001, now U.S. Pat. No. 6,627,269.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to alignment layers for liquid crystaldisplay devices (hereinafter abbreviated LCD). More particularly, itrelates to a photo-alignment material having a photo-reactive functionalgroup of ethenyl at a main-chain, and to the use of that material inliquid crystal displays.

2. Background of the Related Art

Flat panel LCD devices have become widely used as displays for mobileterminals, notebook computers, office equipment, video equipment, andthe like. This is because flat panel LCD devices have advantages ofsmall-size, lightweight, and low power consumption.

In general, an LCD includes a pair of substrates that are separated by apredetermined interval, and an interposed liquid crystal.

An LCD has numerous functional requirements, including lighttransmission characteristics, operational response time, viewing angle,and contrast. Many of those requirements are impacted by the alignmentcharacteristics of the liquid crystal molecules in the LCD. Indeed,uniformly aligned liquid crystal molecules are important to theelectro-optical characteristics of LCDs.

The alignment characteristics of LCDs are results of an alignment layer.Generally, a rubbing technique has been used to form that layer. In thattechnique, a special cloth is rubbed over a substrate to form thealignment layer. While the rubbing technique is a simple process, it hasproblems. For example, various process variables related to rubbing aredifficult to accurately control. Furthermore, dust adsorption, unwantedscratches generated by the rubbing, and damage to thin film transistorscaused by static electricity can also result from the rubbing. Suchproblems reduce the manufacturing yield and the performance of LCDs.

Because of the forgoing problems, significant effort has been expendedin developing alignment techniques that do not use mechanical rubbing.In particular, photo-alignment methods could solve the staticelectricity and dust problems, as well as improve the viewing angle.

Photo-alignment methods include photo-decomposition,photo-polymerization, and photo-isomerization. In these methods, opticalanisotropy is brought about in a polymer layer by inducing aphoto-reaction after most of the molecules facing a polarizing directionin the disorderly-aligned polymer molecules have absorbed light.

In the photo-decomposition method, liquid crystals are arranged byinducing optical anisotropy using a photo-decomposition reaction thatselectively breaks partial bonds of the molecules in a specificdirection by the application of linearly-polarized ultraviolet rays to apolymer layer consisting of a photo-alignment material. The materialtypically used for this method is polyimide. Although polyimide requiresthe application of ultraviolet rays for a relatively long time to induceliquid crystal alignment, a polyimide alignment layer formed byphoto-decomposition has a relatively-high thermal stability as comparedto other photo-alignment layers fabricated by other methods.

In the photo-polymerization method, liquid crystals are arranged bypolymerizing the molecules in a specific direction by applyinglinearly-polarized rays to a polymer layer where polymerization is tooccur.

In the photo-isomerization method, cis/trans isomers are formed by apolarized light. Thus, liquid crystals are aligned by the directiongenerated from the transformation of the produced isomers. Although thealignment direction is reversibly controlled by applying light of aspecific wave length, it is difficult to give a pre-tilt angle to aliquid crystal as well as to maintain the stability of the liquidcrystal.

The chemical structure of photo-alignment materials is mainly dividedinto two categories: a main chain, and side chains includingphoto-sensitive groups such as an alkyl group, an ethenyl group and thelike. The main chain makes liquid crystal molecules arrange to face apredetermined direction, while the side chains form a pre-tilt angle.

Photo-reactions take place at side chains having photosensitive groupswhen light is irradiated onto them. Thus, liquid crystal alignmentdepends on the side chains. Therefore, liquid crystal alignment of thephoto-alignment material is controlled by the side chains, which includehydrocarbon branches such as alkyl, ethenyl and the like.

Unfortunately, related art photo-alignment materials, and LCDs using thesame, have problems. As noted, the photo-alignment of a photo-alignmentlayer according to the related art is controlled by the side chains. Asthe side chains are flexible and fragile, that alignment tends to beeasily broken by thermal, physical, electrical, and photo shocks.Furthermore, the alignment tends to be hard to restore. Additionally,the photo-alignment layer used in the photo-decomposition method hassuch poor photo-sensitivity that relatively high light intensity isrequired to break the predetermined bonds of the side chain or mainchain. Finally, in general, with related art photo-alignment layers theactual liquid crystal alignment is relatively poor.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a photo-alignmentmaterial, to a liquid crystal display device that incorporates thatphoto-alignment material, and to a method of manufacturing a liquidcrystal display device that incorporates that photo-alignment material,wherein that photo-alignment material substantially obviates one or moreof the problems due to limitations and disadvantages of the related art.

Additional features and advantages of the invention will be set forth inthe description that follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages, and in accord with the principlesof the present invention as embodied and broadly described, aphoto-alignment material according to the present invention includes atleast a photo-reactive ethenyl functional group at a polymer main chain.

In another aspect, a liquid crystal display device in accord with theprinciples of the present invention includes a first substrate, a secondsubstrate, a liquid crystal layer between the first and secondsubstrates, and a photo-alignment layer on the first and/or the secondsubstrate. That photo-alignment layer includes an ethenyl group on amain chain of the photo-alignment material.

In another aspect, a method of fabricating a liquid crystal displaydevice according to the principles of the present invention includespreparing a first substrate and a second substrate, forming aphoto-alignment layer having an ethenyl group at a main chain on atleast the first substrate; and forming a liquid crystal layer betweenthe first and second substrates.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying FIG. 1, which is included to provide a furtherunderstanding of the invention and which is incorporated in andconstitutes a part of this specification, illustrates an embodiment ofthe invention and together with the description serves to explain theprinciples of the invention. Specifically

FIG. 1 shows a cross-sectional view of a general liquid crystal displaydevice.

DETAILED DESCRIPTION OF AN ILLUSTRATED EMBODIMENTS

Reference will be made in detail to an illustrated preferred embodimentof the present invention, the example of which is illustrated in theaccompanying drawing. In the illustrated embodiment a liquid crystaldisplay device includes a first substrate, a second substrate, a liquidcrystal layer formed between the first and second substrates, and aphoto-alignment layer formed at least on the first substrate, whereinthe photo-alignment layer is formed from a photo-alignment materialhaving an ethenyl group in a main chain. The alignment stability withrespect to thermal, physical, electrical, and photo shocks is increasedby that photo-alignment layer. More specifically, a photo-alignmentmaterial according to the present invention consists of polymers denotedby the following Chemical Formula 1.

Components ‘A’, ‘B’, and ‘C’ are monomers constituting the polymer andare selectively coupled to produce a homopolymer, a copolymer, or ablock-copolymer. The arrangement order of components ‘A’, ‘B’, and ‘C’is not limited by the above Chemical Formula 1. Furthermore, subscripts‘a’, ‘b’, and ‘c’ denote component ratios between the respectivemonomers, where 0<a≦1, 0≦b<1, and 0≦c<1.

Component ‘A’ is a monomer including a photo-reactive ethenyl group.That component is selected from groups designated in the followingChemical Formula 2, substituted-structure groups of Chemical Formula 2with a halogen, a cyano, a nitro, an amino group and the like, and othersubstituted-structure groups with an alkyl, a haloalkyl, or a cyanoalkylgroup having 1 to 10 carbons, or an aryl, an alkylaryl, a haloaryl, ahaloalkyl aryl, a nitroaryl, or a cyanoaryl group having 3 to 8 carbons.

Components ‘B’ and ‘C’ are selected independently from the followinggroups shown in Chemical Formula 3, substituted-structure groups ofChemical Formula 3 with a halogen, a cyano, a nitro, an amino group andthe like, and other substituted-structure groups with carbonated groupsof which carbon number n lies between 1 and 10 such as an alkyl, ahaloalkyl, and a cyanoalkyl or other carbonated groups of which carbonnumber lies between 3 and 8 such as an alkylaryl, a haloaryl, anitroaryl, a cyanoaryl and the like.

Components ‘B’ and ‘C’, which are non-photosensitive componentsconnected to component ‘A’ regardless of a photo-reactive ethenyl groupof the present invention, increase the reaction of the photo-sensitiveethenyl groups, secures a marginal space for the reaction, or increasesthe reciprocal reaction with liquid crystals.

Therefore, a photo-alignment material according to the principles of thepresent invention is formed by connecting other main chains to a mainchain including a photo-reactive ethenyl group.

The photo-alignment material described above provides a photo-alignmentlayer in which photo-reactivity and alignment stability are improved.

A liquid crystal display device using the photo-alignment materialaccording to the present invention is explained with reference to FIG.1, which shows a cross-sectional view of a liquid crystal displaydevice. Referring to FIG. 1, a liquid crystal display device accordingto the principles of the present invention includes a first substrate 1,a second substrate 2, a liquid crystal layer 3 formed between the firstand second substrates, and a spacer 20 that maintains a uniform intervalbetween the substrates 1 and 2.

The first substrate 1 is a substrate for thin film transistor(hereinafter abbreviated TFT) switching devices that selectively turndata signals on/off in accordance with gate voltages. To that end, onthe first substrate 1 are a gate line having a gate electrode 11 for athin film transistor and a gate insulating layer 12 over the substrateand the gate electrode 11. The gate insulating layer is beneficially asilicon nitride layer (SiNx). A semiconductor layer 13 is on the gateinsulating layer 12 and over the gate electrode 11. A data line 14crosses the gate line. A source electrode 14 a and a drain electrode 14b are on the semiconductor layer 13. A first passivation layer 15 isformed over the substrate as shown in FIG. 1, including over the sourceelectrode 14 a and the drain electrode 14 b. The first passivation layer15 is beneficially of silicon nitride (SiNx) or BCB (Benzocyclo Butene).A pixel electrode 8 that connects to the drain electrode 14 b is formedon the first passivation layer 15. The pixel electrode 8 is beneficiallyof ITO (indium tin oxide). Furthermore, a first alignment layer 4 aextends over the surface, including the pixel electrode 8, as shown inFIG. 1.

The second substrate 2 supports a color filter layer for expressingcolors. On the second substrate 2 are black matrices 16 that preventslight leakage, a color filter layer 17 (RGB) between neighboring blackmatrices 16, and a second passivation layer 18 over the entire surfaceas shown in FIG. 1. The second passivation layer 18 protects the colorfilter layer 17. A common electrode 19 is then formed on the secondpassivation layer 18. The common electrode 19 is beneficially comprisedof ITO (indium-tin-oxide). A second alignment layer 4 b is then formedover the entire surface as shown in FIG. 1.

At least one of the first and second alignment layers 4 a and 4 b isformed from a photo-alignment material that is in accord with theprinciples of the present invention. If the other alignment layer is notformed from a photo-alignment layer material, it can be formed byrubbing.

To form a photo-alignment layer using a photo-alignment material asdescribed above (having an ethenyl group in the main chain), thephoto-alignment material is uniformly coated on a substrate. Thatphoto-alignment layer material is then thermally treated and dried in anoven. Subsequently, a structure that assists anisotropy of the liquidcrystals is attained by irradiating polarized UV rays onto the exposedsurface of the photo-alignment layer. The UV rays may be irradiatedvertically and slantwise using unpolarized light, non-polarized light,linearly polarized light, partially polarized light or the like,depending on the alignment structure to be implemented.

A photo-alignment layer according to the present invention enablesimprovement of the optical and thermal stability of the liquid crystalalignment, pre-tilt stability against electric stress, and improvedshock-resistance. Moreover, the principles of the present inventionenable improved display quality and an improved LCD displaymanufacturing method.

The foregoing embodiments are merely exemplary and are not to beconstrued as limiting the present invention. The present inventions canbe readily applied to other types of apparatuses. The description of thepresent invention is intended to be illustrative, and not to limit thescope of the claims. Many alternatives, modifications, and variationswill be apparent to those skilled in the art.

What is claimed is:
 1. A method of fabricating a liquid crystal displaydevice comprising: preparing a first substrate and a second substrate;forming a photo-alignment layer on the first substrate, wherein thephoto-alignment layer has an ethenyl group in a main chain; and forminga liquid crystal layer between the first and second substrates.
 2. Themethod of claim 1, wherein the photo-alignment layer is formed of amaterial having a photo-reactive ethenyl group on a polymer main chain,wherein the polymer is denoted by the following chemical formula 1:

wherein subscripts a, b, and c denote a component ratio of respectivemonomers, wherein 0<a<1, 0<b<1, and 0<c<1, and wherein component A,which is a monomer including the photo-reactive ethenyl group, isselected from groups designated in chemical formula 2,substituted-structure groups of the chemical formula 2 with a halogen,cyano, nitro, amino group, and other substituted-structure groups withan alkyl and haloalkyl, and cyanoalkyl group having 1 to 10 carbons oran aryl, alkyl, aryl, haloaryl, haloalkyl aryl, nitroaryl, cyanoarylgroup having 3 to 8 carbons;


3. The method of claim 2, wherein components B and C are selectedindependently from groups shown in chemical formula 3,substituted-structure groups of the chemical formula 3 with a halogen,cyano, nitro, amino group, other substituted-structure groups withcarbonated groups of which carbon number n lies between 1 and 10 such asan alkyl, haloalkyl, and cyanoalkyl, and other carbonated groups ofwhich carbon number lies between 3 and 8 such as an alkylaryl, haloaryl,haloalkylaryl, nitroaryl, cyanoaryl;


4. The method of claim 1, further comprising: forming a gate line and acrossing data line on the first substrate; forming a thin filmtransistor at a crossing between the gate and data lines; and forming apixel electrode connected to the thin film transistor.
 5. The method ofclaim 1, wherein the photo-alignment layer is formed bylight-irradiation.
 6. The method of claim 5, wherein thelight-irradiation is irradiated at least once.
 7. The method of claim 5,wherein the light is selected from a group consisting of unpolarizedlight, non-polarized light, linearly polarized light and partiallypolarized light.
 8. A method of fabricating a liquid crystal displaydevice comprising: preparing a first substrate and a second substrate;forming a photo-alignment on the first substrate, wherein thephoto-alignment layer includes an ethenyl group in a main chain; forminga rubbing alignment layer on the second substrate; and forming a liquidcrystal layer between the first and second substrates.
 9. The method ofclaim 8, wherein the photo-alignment layer is formed of material havingat least a photo-reactive ethenyl group at a polymer main chain, whereinthe polymer is denoted by the following chemical formula 1:

wherein subscripts a, b, and c denote a component ratio of respectivemonomers, wherein 0<a<1, 0<b<1, and 0<c<1, and wherein component A, amonomer including the photo-reactive ethenyl group, is selected fromgroups designated in chemical formula 2, substituted-structure groups ofchemical formula 2 with a halogen, cyano, nitro, amino group, and othersubstituted-structure groups with a alkyl and haloalkyl, and cyanoalkylgroup having 1 to 10 carbons or an aryl, alkyl, aryl, haloaryl,haloalkyl aryl, nitroaryl, cyanoaryl group having 3 to 8 carbons;


10. The method of claim 9, wherein components B and C are selected fromgroups shown in chemical formula 3, substituted-structure groups ofchemical formula 3 with a halogen, cyano, nitro, amino group, othersubstituted-structure groups with carbonated groups of which carbonnumber n lies between 1 and 10 such as an alkyl, haloalkyl, andcyanoalkyl, and other carbonated groups of which carbon number liesbetween 3 and 8 such as an alkylaryl, haloaryl, haloalkyl aryl,nitroaryl, cyanoaryl;


11. The method of claim 8, further comprising: forming a gate line and acrossing data line on the first substrate; forming a thin filmtransistor at a crossing between the gate and data lines; and forming apixel electrode connected to the thin film transistor.
 12. The method ofclaim 8, wherein the photo-alignment layer is formed bylight-irradiation.
 13. The method of claim 12, wherein thelight-irradiation is irradiated at least once.
 14. The method of claim12, wherein a light used for light-irradiation is selected from a groupconsisting of unpolarized light, non-polarized light, linearly polarizedlight and partially polarized light.
 15. The method of claim 8, whereinthe rubbing alignment layer is selected from a group consisting ofpolyimide, polyamide, polyamic acid and SiO₂.